The present invention relates to a mold locking device for a molding machine, and particularly to one which takes up relatively small space, and is made with relatively low cost.
A molding machine injects plastic material into a mold with a large pressure. The locking force for the mold must be greater than the injecting pressure of the molding machine, otherwise the plastic material would be pushed out of the mold, making the products have undesirable hairy edges.
Referring to FIG. 6, a conventional molding machine has an oil hydraulic cylinder 20, a toggle assembly 10, a movable mold base 30 and a stationary mold base. The movable mold base 30 and the stationary mold base each holds a respective mold half. The oil hydraulic cylinder 20 extends from the main body of the molding machine for a relatively long distance. The oil cylinder 20 and the toggle assembly 10 move the movable mold base 30 in order to open or close the mold.
However, the molding machine takes up too much space whether in transportation or in use in a factory because the oil cylinder is very long.
To overcome the disadvantage, another conventional molding machine is provided, referring to FIGS. 7, 8 and 9, entitled closing unit for a die in double-toggle machines for the molding of plastic materials or for die casting, with filing number 92830069.8 and Italian patent no. 0511170A2.
The molding machine has a bearing disc 1, a toggle assembly 2, a movable mold base 5, a co-moving disc 3 and two oil hydraulic cylinders 4.
The co-moving disc 3 is movably disposed between the bearing disc 1 and the movable mold base 5. The oil hydraulic cylinders 4 are disposed on the co-moving disc 3 (FIG. 9). The co-moving disc 3 further has a central hole for the toggle assembly to pass through.
The toggle assembly 2 includes two first toggle arms 21, two second toggle arms 22, two third toggle arms 23 and two connecting arms 24. The first toggle arms 21 are pivoted on the bearing disc 1 from outer ends, and pivoted to outer ends of the second toggle arms 22 from inner ends. The second toggle arms 22 are pivoted to outer ends of the connecting arms 24 from inner ends. The connecting arms 24 are connected to the movable mold base 5 from inner ends. The third toggle arms 23 are pivoted to the second toggle arms 22 and the co-moving disc 3 from two ends.
When a cylinder moving rod 41 of the oil cylinder 4 moves forwards, same will force the movable mold base 5 to move forwards. Thus, the movable mold base 5 pulls the connecting arms 24 and the second toggle arms 22 in the same direction; the second toggle arms 22 pivot the third arms 23 inwardly of the toggle assembly 2 to push the co-moving disc 3 and the cylinders 4 forwards. When the toggle assembly 2 is moved to a substantially straight position, the mold is closed (FIG. 7).
The second conventional molding machine takes up less space than the first one because the oil cylinders are received between the bearing disc 1 and the movable mold base 5. However, the mold machine has relatively high cost because it needs two oil cylinders on two side of the co-moving disc for the toggle assembly and the movable mold base to move smoothly.
Therefore, it is a main object of the present invention to provide a molding machine which can overcome the disadvantages of the above-mentioned molding machine.
The mold locking device for a molding machine of the present invention includes a toggle assembly, and a transmission.
The toggle assembly includes two first toggle arms, two second toggle arms, two third toggle arms and two connecting arms. The first toggle arms are pivoted to a bearing disc of the molding machine. The second toggle arms are each pivoted to a respective one of the first toggle arms from one end. The third toggle arms are each pivoted to an intermediate portion of the respective second toggle arm from one end, and pivoted to a co-moving disc of the molding machine from other end. The co-moving disc has a nut turnably fitted to a central portion.
The connecting arms are each pivoted to the respective second toggle arm, and a movable mold base of the molding machine from two ends. The movable mold base is provided for one of two halves of a mold to be held on.
The transmission member includes a power, an elongated screw and a connecting member. The connecting member connects the power and the nut of the co-moving disc. The elongated screw is turnably passed through the nut, and connected to the movable mold base. When the transmission member is started for the nut to turn in a first position, the nut moves forwards along the screw, pushing the co-moving disc, and the movable mold base forwards, moving the toggle assembly to a mold closing position to close the mold.
Only one transmission member is needed in place of two oil cylinder so the molding machine has relatively low cost.